$$ \mathrm{ATP} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{ADP} + \mathrm{P}_i + \text{energy} $$

Question 1

Which molecular event directly causes the power stroke in the sliding filament model of skeletal muscle contraction?

Accepted Answer

Release of ADP and Pi from the myosin head

Question 2

At the neuromuscular junction, which ion's influx into the presynaptic terminal triggers the release of acetylcholine?

Accepted Answer

Ca$$^{2+}$$

Question 3

During muscle contraction, what is the role of tropomyosin?

Accepted Answer

It covers myosin binding sites on actin at rest

Question 4

Which sequence correctly describes the events at the neuromuscular junction leading to muscle contraction?

Accepted Answer

Action potential arrives, Ca$$^{2+}$$ enters, acetylcholine released, acetylcholine binds receptors, Na$$^{+}$$ influx, muscle action potential

Question 5

Which equation best represents the ATP hydrolysis reaction that energizes the myosin head during muscle contraction?

Accepted Answer

$$ \mathrm{ATP} + \mathrm{H}_2\mathrm{O} ightarrow \mathrm{ADP} + \mathrm{P}_i + 	ext{energy} $$

Question 6

A patient is exposed to a toxin that blocks acetylcholine receptors at the neuromuscular junction. What is the most likely effect?

Accepted Answer

Muscle contraction will be inhibited

Question 7

Which of the following best explains how motor unit recruitment allows for gradation of skeletal muscle contraction strength?

Accepted Answer

Activating more motor units increases the total number of muscle fibers contracting

Question 8

Which statement about the sliding filament model is correct?

Accepted Answer

Actin and myosin filaments slide past each other, shortening the sarcomere

Question 9

If a muscle fiber is unable to release Ca$$^{2+}$$ from the sarcoplasmic reticulum, which step in contraction will be directly affected?

Accepted Answer

Myosin binding to actin

Question 10

A muscle is required to generate a very fine, precise movement. Which motor unit recruitment strategy is most likely used?

Accepted Answer

Recruitment of small motor units first

Question 11

Which of the following is the correct order of events in the cross-bridge cycle?

Accepted Answer

Myosin binds actin, power stroke, ATP binds myosin, myosin detaches

Question 12

Which neurotransmitter is released at the neuromuscular junction to initiate skeletal muscle contraction?

Accepted Answer

Acetylcholine

Question 13

A person is unable to perform strong muscle contractions but can still perform weak ones. Which physiological process is most likely impaired?

Accepted Answer

Motor unit recruitment

Question 14

Which of the following best describes the role of troponin in muscle contraction?

Accepted Answer

Troponin binds Ca$$^{2+}$$, causing tropomyosin to move and expose myosin binding sites on actin

Question 15

Which of the following would most likely increase the strength of a whole-muscle contraction?

Accepted Answer

Recruiting additional motor units

Question 16

A patient with myasthenia gravis has reduced acetylcholine receptor function. Which symptom is most likely?

Accepted Answer

Muscle weakness due to impaired neuromuscular transmission

Question 17

Which process is directly responsible for the termination of muscle contraction at the cellular level?

Accepted Answer

Reuptake of Ca$$^{2+}$$ into the sarcoplasmic reticulum

Question 18

If the acetylcholinesterase enzyme is inhibited at the neuromuscular junction, what is the expected effect?

Accepted Answer

Prolonged muscle contraction due to continued acetylcholine action

Question 19

Which of the following best describes the relationship between the number of motor units recruited and the force of muscle contraction?

Accepted Answer

Force increases as more motor units are recruited

Question 20

Which of the following is NOT a direct component of the sliding filament model?

Accepted Answer

Acetylcholine

Skeletal Muscle Contraction: Cellular and Organ-Level Mechanisms

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